Since the early 1970s, very large numbers of hamburgers and other food patties have been produced by large, high speed, high volume food patty molding machines. In these machines, a mold plate having a plurality of mold cavities that extend through the plate is moved reciprocably between a fill position and a discharge position at high cyclic rates, as high as ninety cycles per minute. At the fill position, ground meat or other food product is pumped into the cavities in the mold plate to form food patties. At the discharge position, knockout cups push the food patties out of the mold plate onto a takeaway conveyor.
The prototype for machines of this kind, and probably the fastest, highest volume commercial food patty molding machine, is the machine described and claimed in Richards U.S. Pat. No. 3,887,964, issued June 10, 1975, subsequently replaced by U.S. Reissue Patent No. Re. 30,096 issued Sept. 18, 1979. That particular machine has been commercially available from Formax, Inc. of Mokena, Ill., first as the Model F-24 machine and currently as the Model F-26 machine. The Richards machines utilize hydraulic drives for the food pumps and for other machine functions. In commercial practice, these machines have employed electric drive motors for reciprocation of the mold plate, but hydraulic drive motors could also be used. Other commercially successful machines of this general type are disclosed in Sandberg et al U.S. Pat. No. 4,054,967 issued Oct. 25, 1977 and LaMartino et al U.S. Pat. No. 4,182,003 issued Jan. 8, 1980.
In the Formax F-26 machines, as disclosed in U.S. Pat. No. 3,887,964 and as made and sold commercially, a hydraulic cylinder has been incorporated in a drive linkage for the reciprocal mold plate, between the mold plate and a prime mover. This hydraulic cylinder has a dual purpose; it serves as a shock absorber for the mold plate, which has substantial weight and which must accelerate and decelerate rapidly in moving back and forth between its fill and discharge positions. The hydraulic cylinder also serves to establish momentary stationary "dwells" for the mold plate at both its fill position and its discharge position. This is done to allow time for filling of the mold cavities at the fill position and for discharging the completed food patties at the discharge position. The hydraulic cylinder in this linkage has been connected to a small local fluid reservoir, and hydraulic fluid has been supplied to the cylinder from the reservoir by the pumping action of the movement of the piston within the cylinder.
This hydraulic cylinder drive linkage of U.S. Pat. No. 3,887,964 and the commercial Formax F-24 and F-26 machines, however, has been a continuing source of technical difficulties since the first machines went into service in the early 1970s. Any leakage from the cylinder itself or from any of the connections to the local reservoir rapidly depletes the small oil supply in that reservoir. When this occurs, the cylinder begins to "hammer" and rapidly self-destructs. The hydraulic cylinder and its oil reservoir cannot dissipate heat adequately. Nor is it possible to have effective filtering to preclude contamination of the hydraulic fluid from metal particles or water. The lack of heat dissipation results from the small size of the hydraulic fluid reservoir and the small volume of hydraulic fluid that is displaced in each cycle of the piston in the cylinder. The small quantity of oil movement and the reversal in its direction of movement makes effective filtering quite difficult. Effective maintenance is also inhibited by the fact that the oil reservoir is quite small; maintenance personnel have a tendency to fill it with whatever oil or other substance is most readily available.